1. Field of the Invention
The present invention relates to a biometric identification technique, and in particular to a biometric data acceptance method for use in biometric identification.
2. Description of the Related Art
In network-based information services, identification of individuals is one of the most important issues to ensure protection of communications security against abuse, unauthorized use, tempering by unauthorized persons, pretending to an authorized person, or the like. The identification must be accurate but not too cumbersome. To meet such a condition, there have been proposed a number of biometric identification techniques. Biometric data is data representing a certain human characteristic that is not changed over all one's life and is different from person to person, typically fingerprints, hand geometry, retinal scans, facial images and the like.
Taking fingerprint identification as an example, a user places his/her predetermined finger on a prism so as to display its fingerprint to a scanner such as a CCD image sensor. The input fingerprint image data is sent to a fingerprint verifier, in which feature data is extracted from the input fingerprint image data and then it is compared against previously stored fingerprint feature data. Since a fingerprint is a unique and distinctive pattern that presents unambiguous evidence of a specific person, accurate and simple identification of individuals can be achieved. Such a fingerprint identification system has been disclosed in Japanese Patent Application Unexamined Publication No. 4-33065.
In the above-described fingerprint identification system, it is necessary to previously register the feature data of a reference fingerprint that is used for comparison. In general, the scanner scans a user's finger on a prism to produce fingerprint image data and, if the number of pixels having gray levels greater than a predetermined gray level exceeds a predetermined value, it is determined that the input fingerprint image data is acceptable.
In order to register the reference fingerprint with reliability, the user's finger is usually scanned a plurality of times. A plurality of input fingerprint images obtained by the scanning operations are used to create the feature data of the user's fingerprint. For example, an input fingerprint image having the best quality is used to extract its feature data. Alternatively, a combination of several input fingerprint images may be used to create the feature data more suitable for comparison.
Such a fingerprint input method imposes the user to perform the fingerprinting operation a plurality of times. More specifically, the user must repeatedly place the finger on the scanner and move it off the scanner plural times to produce fingerprint patterns caused by different fingerprinting operations.
However, there may be cases where some user continuously places the finger on the scanner without moving it off to produce input fingerprint images by scanning it plural times. In such a case, the correct fingerprinting operation is not performed and therefore the fingerprint data obtained by such an incorrect fingerprinting operation should not be accepted.